Process for producing large well-formed crystals from solutions of different kinds.



.J. BOOK.

PROGESS FOR PRODUCING LARGE WELL FORMED CRYSTALS FROM SOLUTION S OFDIFFERENT KINDS. APPLICATION FILED MAY 13, 1908.

Patented Feb. 21, 1911.

JOHA'NNES 300K, or RADEBEUL, NEAR nmisnniv, GERMANY.

PROCESS FOR PRODUCING LARGEWELL-FORMED CRYSTALS FROM DIFFERENT KINDS.

SOLUTIONS OF Specification of Letters Patent.

Patented Feb. 21, 1911.

To all whom it 'may concern:

, Be it known that I, JOHANNES BooK,

chemist, a subject of the German Emperor, residing at 29 Bennostrasse,Radebeul, near Dresden, Germany, have invented certain new and usefulImprovements in Processes for Producing Large Well-Formed Crystals fromSolutions of. Different Kinds; and I do hereby declare the following tobe a full, clear-,and exact description of the invention, such as willenable others skilled in the art to which it appertains to make and usethe same.

It is well known that for the production of well formed crystals from asolution a certain overconcentration and agitation of the crystallizingsolution is necessary. The

overcon'centration is essential'in order that the separation of thesubstance from the solvent can take place, and the agitation is atfected in order that new portions of the supersaturated crystallizingsolution may come into contact with the crystals present, whereby acontinuous and uniformly progressive enlargement of the crystals is madepossible, because then the material separating out is taken up by thecrystals without the formation of new crystals. In order, however, tomake sure of this separation'of the substance on the crystals present inthesolution, the concentration must not exceed a certain predeterminedlimit, that is, the

separation must not proceed so quickly that.

the crystals present, on which in a definite time only a definitequantity of the substance crystallizes, are not any longeF in acondition to take up the substance which is being separated out; in sucha case a new formation of very smallcrystals or, slimy substances takesplace, and thus the desired effect is lost. It has been sought toprevent this result by a cooling process, the crystallizing-materialbeing agitated on the one hand by suitable mechanism means such as astirring apparatus, while on the other hand the cooling off is-suitablyregulated. The

cooling must be effected so slowly that the substance which as a resultof the cooling off of the mother liquoris separated out, will be takenup by the crystals. When the crystallization is carried out byevaporation, the new formation of small crystals is prevented byeffecting the evaporation very slowly,

with the addition oft new solution at long 1 intervals.

Heretofore the regulation of the crystallization by the known means andapparatus, to the desired extent, has been impossible. If the coolingoil or the evaporation proceeds so fast that it does not correspond tothe taking up capacity of the crystals present, the separation of newcrystals takes place immediately. The desired enlargement of the firstcrystals does not then occur and the entire operation becomes .useless.After the dissolving of the crystals, the crystallizing operation mustbe started a ain at the beginning. It is necessary, there ore, inefiecting'the crystallizing out of solutions, especially when largecrystals are to be formed, to'proceed in such a way that thecrystallization is maintained far under the taking up capacity. of thecrystals present, wherefore if the crystallization be produced byevaporation, (which heretofore, moreover, has only been employed for theproduction of small crystals), the hot vapor of the heating body is usedin such small quantity that the slow removal of the solvent isaccomplished. This vaporized solvent is a jet condenser, and runs awaywith the cooling water, which is conducted to such condenser. There hastherefore been, heretofore, no means for effecting the crystallizationby evaporation,- in such a manner that the progressive separation of thesubstance takes place uniformly in a desired quantity, Whichquantity'can be altered according to the wish of the. operatoni One hasnot been in a position to hasten the crystallization and thereby effectthe growing of only the crystals at hand; and still less has any meansbeen known to carry the crystallization up to the optimum of the takingup capacity of the crystals which are at hand when the operation iscommenced. The present invention has for its object the growth of wellformed individualcrys,

tals up to a considerable size, by the evaporation process,'in such away that the crystallizingof the substance is so regulated that in adefinite time unit a desired and, known quantity of substancecrystallizes out, this quantity being alterable as desired, and finallyso that the crystallization'is regucreate or infiuencethecrystallization conditions themselves advantageously.

It is known that the formation of vapor in the crystallizing solutionitself'is a very appropriate means of effecting the agitation which isnecessary for the crystallization of the material in solution. Thismeans is therefore utilized in carrying out my invention. However, inaccordance with this invention the vapor is condensedin a suit- 1 ablecondenser, preferably a surface condenser, and the condensate, ifnecessary, is then wholly or in part conducted back again to thesolution. In this manner it is possible to make the agitation in themass as reat as desired, without thereby removing from the crystallizingsolution more of the solvent than corresponds to the quantity ofsubstance which the crystals can take up. It is therefore possible toevaporate thesolution quickly and far above the degree which hasheretofore been permitted, for that quantity of solvent which isvaporized too quickly is led back into the solution, and only so much ofthe entire condensate is separated out as corresponds to the quantity ofsubstancewhich the crystals can take up. In other'words, one is inaposition, with this procedure, to initiate and maintain a definite anddesired concentration in the solution in spite of a Very powerfulevaporation.

As the quantity of substance present in the solution at any given timeis known, it can be readily determined how much substance in a certaintime unit-can be taken up 40 bythe crystals present, and hence throughthe removal of a corresponding quantity of condensate it is possiblealso to accomplish the desired crystallization on the crystals ofadefinite quantity of such substance. It

is therefore possible, by observation, to raise the separation of thesubstance and its crystallization on the initial crystals to the optimumof the taking up capacity of the latter,w1thout danger of bringing abouta new formation of crystals.

' The improved method also accomplishes a regulation of the temperaturewith a view to creating the most favorable crystallization conditions. Ihave found that the crystallization of well formed crystals, viz., the

growth of the same, is eflectedmost favorably and most rapidly at adefinite temperature. I On the one hand ,there comes into question theviscosity of thesolution, which 0 tends to prevent crystallization andwhose influence is augmented at definite temperatures, On the otherhand, the movability of the molecules, which plays a certain part in thecrystallization, is likewise influenced by the temperature, andtherefore at a predetermined temperature, which varies with differentsubstances, the most favorable conditions for the crystallization, andtherefore for the building of large well formed crystals, 'can beobtained. The maintenance of a definite temperature in crystallizing byevaporation is necessary, moreover, with such substances as crystallizeout of their solutions at different temperatures with different contentsof water. Again, the tem perature of the solution plays a part in therecovery of the material as it determines the different solutionconditions and therefore the evaporation crystallization should beconducted at that temperature at which the best recovery, with theformation of large crystals, is guaranteed. As the crystallization isaccomplished by evaporation in accordance with this invention, thatcrystallization temperature is selected as evaporating temperature whichpermits the production of good, well formed crystals most favorably. Inorder now to make the evaporation temperature correspond to the bestcrystallization temperature, in carrying out the crystallization byevaporation of the solvent, with the regulation of the rapidity withwhich the crystals grow,-. as previously described, the crystallizationof the solution is effected under that pressure (vacuum, atmosphericpressure or overpressure), by which the desired temperature is producedin the solution. By altering the pressure the boiling temperature can'bealtered, as is well understood. It is therefore possible by thealteration and discontinuance of the pressure, which is maintained overthe heated solution in the most uniform manner, to reach the optimum ofthe temperature for the growth of-the crystals. Moreover, one is furtherin a position to maintain the necessary high crystallizing temperaturein the crystallization of substances out of solutions which boil at lowtemperatu'res, e. 9., ether, be'nzin and the like, by placing acorresponding overpressure on the cooking solution and thereby arrivingat the desired high temperature which is necessary for a goodcrystallizing' efi'ect- As previously explained, the condensate of thevaporized solvent may be either wholly or partially returned to thesolution, so much of the condensate being removed as corresponds to. thequantity of substance which the crystals can take up. In order toascertain this quantity of condensate, the following procedure isnecessary :By experiment it is first ascertained what quantity of thesubstance the crystals which are to be grown can take up in a certain,time unit at the necessary temperature or any temperature which is beingmaintained. It is also determined what quantity of the substance issoluble in a definite quantity of the the one hand, the formation of newcrystals, so much of the solvent.

and, on the other, must be removed, nevertheless, as the crystals are ina position to take up. If more solventis evaporated out of the solutionthan corresponds to the quantity of substance which will grow ontheerystals, the surplus quantity of condensate must be returned. Thisis effected by recovering the condensate, measuring the quantity of thesame, carrying oifthe calculated quantity, and conducting back to thesolution the remaining part. If this procedure is followed one is evenin a position to so control the rapidity of the evaporation of thesolvent by the regulation of the heating medium, that only so much ofthe solvent .will be vaporized as corresponds to the quantity ofsubstance which will grow on the crystals.

In this case it is especially recommended that the agitation of thesolution be augm'ented by a rocking orjshaking movement of the apparatusor the stirring 'of the solution by means of stirrers or the like.

. As after a certaintime a considerable part of the substance present inthe mother liquor is crystallized out, it is necessary to add newsubstance to such liquor in order thatcrystals of the largest size maybe grown. According to the present process this is effected bydissolving the additionalsubstance in that part of-the condensate whichflows back to the solution. As. it is known bydetermin-ing the quantityofcondensate,'how much of the substance has crystallized out,

to be supplied to the solution in. order to correspond with the rapidity"with which the substance is taken up by the crystals. Quantities of]substance which have been measured or ,weighed or otherwisedeterminedcan be dissolvedin the condensate,

or a definite part of the condensate can be run through a quantity ofthe substance in order to form 1n this way a solution of the feedingsubstance and bring it into the crys' solution. Obviously a correspond-'ing quantity-of the same solvent from an tallizing Instead of'dissolvingthe feeding sub;

stance in the condensate, fresh feeding solution can be introduced intothe crystalliz taken out of circulation,

' then taken u it" is possible to determine ere actly the amount of thesubstance which is.

ing solution in order thatthe growth of the crystals can be carried onas long as desired. In this case tals correspond to the maximum rapiditywith which they can be grown, as explained, and a definite quantity ofthe substance must be separated out on the crystals in the time alsomust the growth of the crysunit, for which reason such a quantity ofsolvent must be removed fromthe condensate as corresponds to thatbrought into the apparatus in the feeding solution. As a consequence,the solvent vaporized out of the crystallizing mass as condensate iseither measured or weighed, and in the same time unit the same quantityof solvent is led into the crystallizing apparatus as that :inwhich issoluble the quantity of substance which the crystals can take up inthetime unit.

Or, a measured quantity of condensate is and correspondinglya likequantity of solvent with thesubstance dissolved-therein can be added. Bythis process a perfectly continuous and automatic cycle of operations isprovided.

The following examples will illustrate several modes ofprocedure fallingwithin the general process :In a crystallizing apparatus which isconnected with a surface condenser and an air pump, 5 kilograms,

say, of crystals are introduced, and from 6 to 8 kilograms ofconcentrated solution are The solution is then evapothe vapo-1- addedthereto. rated by heating the apparatus, ized solvent being condensed'inthe surface condenser, and the so formed condensate is in part in ameasuring receptacle, the ot er part being returned to the apparatus. Ithas been previously determined, for example, that the qu'antityof',crystals introduced into the apparatus "can take up in an hour about 3%of its weight,

viz., 150 gr.- of the substance. In order to form this quantity hourlyon the crystals already present, such aquantity ofsubstance is dissolvedin water, e. 9;, 300 gr. of water, and. this feeding solution iscontinuously or intermittently introduced into the apparatus during anhour. At the same time 300 gr. of condensate are collected in themeasurreceptacle and thus taken out of circu- 1n 'la ion, while theremaining part of the condensate is returned to the apparatus. As in anhour 150 gr. of substance and 300 of water are fed into the apparatus,while 300 gr. of water are led off ascondensate, the 150 gr. ofsubstance will crystallize on the crystals present. The processcan alsobe carried through in such a Way that by regulating-the heating of theapparatus only 300 gr. of condensate are produced, measured and carriedoff. In

, this case the heating is regulated by measur-.

ing the condensate. The process can also be carried out without theregulation of the heating but with measuring and carrying oil sary tolead back all it is to be understood that a proper crystallization underthese conditions takes place only when the quantity of additionalsubstance in the feeding solution corresponds to that which the crystalspresent are ableto take up in the time unit, as any surplus of suchsubstance will form new crystals. In

this connection, it should be remarked that as certain substances incrystallizing take up water of crystallization, this must be compensatedfor in feeding in solvent to-maintain the concentration of the solution.In some cases, as intimated above, it is necesof the condensate to theapparatus, even when additional feeding substance isnot' fed into thelatter or is supplied only intermittently. The first or initial crystalswhich are to be used can be generated in the known manner from thesolution itself and will then be left to grow therein, or othercrystals, crystal meal or crystal fragments may be introduced into thecrystallizing solution. The ordinary crystallizing a paratus and surfacecondensers may be used in carrying out the improved method, thedetermination of the quantity of condensate being ascertained by anappropriate measuring receptacle or asuitable weighing apparatus.

. In the drawing, have illustrated schematically one form of apparatusfor carrying out the method, but 1t is to be understood that theparticular form of apparatus is entirely immaterial to the invention.

Referring to the drawing a indicates a closed crystallizing apparatus,which 1s provided with a double bottom 6 to which heat is applied in asuitable manner, and o is the inlet pipe for the solution to becrystallized and also for'the condensate which is led back to theapparatus. The side walls of the apparatus are removable or providedwith closable openings in order that the finished product may be removedfrom the apparatus. with the crystallizer o'by'means of a connection (Ithrough which the vapors from are conducted to the conthey arecondensed. The

from the condenser 0 through .the pipe f into the measuring receptacle9, wherein such condensate is measured. The condensate then passes fromthe measuring receptacle either wholly or partially through the pipe hto the dissolving receptacle 1' in which the fresh substance to becrystallized is introduced.- In passing through the latter receptaclethe condensate is saturated with the aforesaid substance thecrystallizer denser, wherein condensate passes and passes through thepipe is into the crys-- tallizer a. The pipe Z serves for conducting thecondensate from the measuring recepreceptacle by A surface condenser eis connected tacle directly to the crystallizer, the condensate to beremoved or taken out of circulation being conducted away from said meansof the pipe m. The pipe n serves 'to introduce fresh solution into thecr stallizer. Theconnections are provided with shut-off. cocks and airinlets, as indicated.

The vessel a is preferably mounted to swing upon arms g in order that itmay be agitated. The arms 9 are hung loosely from the two ends of arocking bars fixed to the rock shaft 1' to which a rocking motion isimparted. by the arm w. The arm w isattached to the rock shaft 1' and isitself actuated by a rod t which is connected to the strap of aneccentric u fixed upon a rotary shaft v. The rotation of the lattershaft imparts a reciprocating motion to the rod t, thereby oscillatingthe vessel a, and, in order to permit this oscillation, said vessel isconnected with the upper and lower pipes by the flexible pipe sections 0and 2.;

The double'bottom b is preferably heated by circulating hot water in thesame, which water may conveniently be passed through a preheater afterleavin the apparatus, and thus brought to the esired temperature,whereupon it may be returned to the double bottom by means of a suitablepump.

The process can be carried out with any desired crystallizablesubstance, whether it be organic or inorganic in character.

What I claim is 4 1. A process of obtaining crystals from solutions,which comprises evaporating the solution at such a pressure as toproduce the optimum crystallizing temperature, condensing the vaporsgiven off from the solution, measuring the condensate, and maintainingthe concentration of the solution as called for by the ratio between therate of condensate formation and the rate of crystallization;substantially as described.

2. A process of obtaining crystals from solutions,'which comprisesevaporating the solution at an appropriatepressure, collecting thevaporized solvent as condensate, measuring such condensate, maintainingthe concentration of. the solut1on as called for by the ratio betweenthe rate of condensate formation and the rate of crystallization, andadding additional solvent and crystal lizable material in suchroportions as not to disturb the fixed ratio of solvent andcrystallizablei"material prevailing in the evaporating vessel;substantially as described.

3. A process of obtaining crystals from solutions, which comprisesevaporating thesolution at an appropriate pressure, withdrawing from theeva orating vessel, in a time unit, so much of t e vaporized solvent, ascondensate, as will dissolve to saturation the quantity of substancecrystallized out in 0 such a time unit, and adding solvent andcrystallizable' substance to the solution in such quantity andproportions asto maintain the existing concentration; substantially asdescribed.

4. A process of obtaining crystals from solutions, which consists inevaporating the solvent of the solution ata predetermined pressure andtemperature appropriate to the formation ofthe particular crystalsdesired, and returning so much of the evaporated solvent to the solutionas shall maintain therein a fixed ratio between the amount of thesolvent and of the crystallizable material; substantially as described.

5. A process of obtaining crystals from solutions, which consists inevaporating the solvent of the solution at a predetermined pressure andtemperature appropriate to the formation of the particular crystalsdesired,

returning so much of the evaporated solvent to the solution as shallmaintain therein a fixed ratio between the amount of the solvent and ofthe crystallizable material, and supplying an additional quantity ofsolvent and crystallizable material in such proportions as not todisturb the said fixed ratio prevailing in the evaporating vessel,thereby making the OPGI'iltlOIl'COIItlIlHOUS; substantially asdescribed.

6. A process of obtaining crystals from solutions, which consists inevaporating the solution, recovering the vapors as condelr sate, andreturning to the solution, during a unit of time, that part of thecondensate in excess of the amount in which the material crystallized insuch a time unit is soluble 'to saturation; substantially as described.

7. A process of growing crystals in solutions agitated by steam producedin the solution itself, which consists in condensing the evaporatedsolvent, dissolving in the condensed liquid the substance to bedeposited on the crystals, and returning the resulting solution into thecrystallizing solution; substantially as described. 8. A rocess ofgrowing crystals in solutions, w erein the solution is agitated bygenerating vapor therefrom, A and wherein the vaporized solvent is usedto d ssolve the substance to be grown onthe crystals, whereupon the aresulting solution is conducted back to the crglgtallizing solution;substantiall'y as descri :9. A process for the recovery of largecrystals from solutions, wherein the solution is evaporated at atemperature and pressure appropriate to the formation of the desiredcrystals, and wherein the vapors are recovsponding to the quantity ofmaterial separated out and the quantity of condensate collected;substantially as described.

11. A process for the recovery of large crystals fronrsolutions, whereinthe solution is vaporized at an appropriate pressure, and wherein thevapors are recovered as condensate, the concentration of the solutionbeing regulated by conducting back to the solution that part of thecondensate which exceeds the proportion between the substance separatedout and the corresponding quantity of solvent; substantially asdescribed.

12. A process for the recovery of crystals from solutions, wherein thesolution isvaporized at an appropriate pressure, and wherein thevaporized solvent is condensed and removed, the concentration of thesolution being regulated by conducting back to it a part of thecondensate formed, and dissolving in such part of the condensate theadditional quantities of substance to be crystallized; substantially asdescribed.

In testimony whereof I have afiixed my signature, in presence'of twowitnesses.

J OHANNES BOCK.

Witnesses WOLDEMAR' Haurr, HENRY HAsrnR.

